This section provides background information related to the present disclosure which is not necessarily prior art. This section also provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.
Sensors, such as gas sensors used in automotive vehicle systems, can include elements that are susceptible to excessive thermal stress that can result in failure of the sensor. These sensor elements can be heated and, as a result, if the heated element comes in contact with a fluid of a lower temperature, thermal stress can be created in the element. The thermal stress may lead to degradation in performance or failure. By way of non-limiting example, such gas sensors can include oxygen sensors, air/fuel sensors, and NOx sensors used in the exhaust systems of automotive vehicles. These gas sensors include elements that are heated to an operating temperature to perform their intended function. The heated sensor elements are exposed to the exhaust gases flowing through the exhaust system. Water vapor in the exhaust streams may condense in the exhaust system and/or on the sensor during some operating conditions. One such operating condition can include operation under winter conditions. Due to the elevated temperature of the sensor element, if the water droplets were to come in contact with the element, thermal stress can occur. Excessive thermal stress can lead to damage to the element and degradation in performance or failure of the sensor. Accordingly, it is advantageous to minimize the possibility of water droplets in the exhaust system from contacting the sensor element to reduce the potential for thermal stress.
A protective heated screen for an element of a sensor, according to the present teachings, surrounds a portion of the element and reduces and/or minimizes the propensity for water droplets to come in contact with the heated element. The screen can allow fluid flow therethrough to allow the sensor element to come in contact with the fluid stream, thereby allowing the sensor to perform its intended function. The screen can be in continuous heat-transferring contact with the sensor element such that both the sensor element and screen are at a temperature significantly greater than the ambient temperature. The screen can be a mesh that allows gaseous fluid to flow therethrough. Water droplets contacting the heated screen may evaporate such that the liquid water droplets do not come in contact with the sensor element. The screen can also break down the water droplets into smaller droplets such that the thermal stress created by the water droplets contacting the heated element is reduced over that caused by a larger water droplet.
A gas sensor according to the present teachings includes a gas-sensing element operative to detect a concentration of a specified gas in a gas flow. A heating element is operative to heat the gas-sensing element to an operating temperature. A housing supports the gas-sensing element. A screen with a plurality of ventilation openings is disposed exterior to the gas-sensing element. The screen surrounds the leading end portion of the gas-sensing element such that a gas flow travels through the ventilation openings prior to reaching the gas-sensing element. A first portion of the screen is in continuous direct heat-transferring contact with the gas-sensing element such that heat generated by the heating element is transferred to the screen through the gas-sensing element. A second portion of the screen is spaced apart from the gas-sensing element with a first gap therebetween.
A method of operating a gas sensor to detect a concentration of a specified gas in a gas flow while reducing a possibility of liquid droplets contacting the gas-sensing element according to the present teachings includes surrounding a leading end portion of the gas-sensing element with a screen having a plurality of ventilation openings and disposed exterior to the gas-sensing element such that the gas flow travels through the ventilation openings prior to reaching the gas-sensing element. The screen having a first portion in continuous direct heat-transferring contact with the gas-sensing element and a second portion spaced apart from the gas-sensing element with a first gap therebetween. The method includes heating the gas-sensing element to an operating temperature with a heating element and heating the screen to an operating temperature with heat transfer from the gas-sensing element to the first portion of the screen. The method includes evaporating liquid droplets in the gas flow that contact the screen and detecting the concentration of the specified gas in the gas flow.
Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.